From: Eric Dumazet <dada1@cosmosbay.com>
To: Stephen Hemminger <shemminger@vyatta.com>
Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org
Subject: Re: [RFC] loopback: optimization
Date: Thu, 06 Nov 2008 00:14:16 +0100 [thread overview]
Message-ID: <491228C8.3010100@cosmosbay.com> (raw)
In-Reply-To: <20081105123659.6045b216@extreme>
Stephen Hemminger a écrit :
> Convert loopback device from using common network queues to a per-cpu
> receive queue with NAPI. This gives a small 1% performance gain when
> measured over 5 runs of tbench. Not sure if it's worth bothering
> though.
>
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
>
> --- a/drivers/net/loopback.c 2008-11-04 15:36:29.000000000 -0800
> +++ b/drivers/net/loopback.c 2008-11-05 10:00:20.000000000 -0800
> @@ -59,7 +59,10 @@
>
> +/* Special case version of napi_schedule since loopback device has no hard irq */
> +void napi_schedule_irq(struct napi_struct *n)
> +{
> + if (napi_schedule_prep(n)) {
> + list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list);
> + __raise_softirq_irqoff(NET_RX_SOFTIRQ);
> + }
> +}
> +
Stephen, I dont get it.
Sure loopback device cannot generate hard irqs, but what prevent's a real hardware
interrupt to call NIC driver that can call napi_schedule() and corrupt softnet_data.poll_list ?
Why not using a queue dedicated on loopback directly in cpu_var(softnet_data) ?
(ie not using a napi structure for each cpu and each loopback dev)
This queue would be irq safe yes.
net_rx_action could handle this list without local_irq_disable()/local_irq_enable() games.
Hum, maybe complex for loopback_dev_stop() to purge all queues without interfering with other namespaces.
next prev parent reply other threads:[~2008-11-05 23:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-04 5:37 [RFC] loopback: optimization Stephen Hemminger
2008-11-04 6:36 ` Eric Dumazet
2008-11-05 9:49 ` David Miller
2008-11-05 20:36 ` Stephen Hemminger
2008-11-05 23:14 ` Eric Dumazet [this message]
2008-11-06 0:42 ` Stephen Hemminger
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